This invention relates to a stabilized mount system for radio antennas. More specifically, this invention relates to a purely mechanical stabilization system for mounting radio antennas, such as those used in cellular telephone systems on vehicles such as ships.
Typically, vehicles such as ocean going ships are subjected to motion, such as roll, pitch and yaw, caused, for example, by result of wave motion, gusting winds, and the acceleration, deceleration and turning of the vehicle. Often, a ship may be subject to pitch and roll movements in the order of .+-.20.degree., depending on the size of the ship and the loading conditions. Many ocean vessels come equipped with stabilizers to assure that the movement does not exceed .+-.20.degree..
In conventional antenna systems (see FIGS. 10 through 13), uniform signals are transmitted from a single source point, with gain and bandwidth being varied to adapt to the application. An ocean vessel antenna system requires high gain to minimize power requirements. Referring to FIG. 11 and FIG. 12 it may be seen that as an antenna's gain increases, the beam width narrows and the allowable limits on the physical orientation of the antenna decrease. Further, as shown in FIG. 13, without a stabilization system, the combination of a narrowed beam width and the roll, pitch, and yaw of a ship can cause a radiated signal from the antenna to intersect the surface of the water or to otherwise reach an undesirable-cell site location. Therefore, an effective antenna stabilization system must compensate for the roll, pitch and yaw of the ship, and also act to decouple the transmission and reception characteristics of the antenna from the movements of the ship.
Many conventional antenna stabilization systems are electronically controlled and/or electrically driven. These systems often include gyroscopes, servomotors, microprocessors, and various forms of feedback circuits. Commonly, stabilization devices use gyros in combination with multi-access integrators, in order to stabilize a platform system. The passive stabilization system is further controlled by a feedback loop, which interacts with motors to assure that the system is continuously stable by moving the gyro and pendulum weight as needed. Other devices make similar use of the electronic controls, but use a pendulum connected to a spring or a ring mounted for rotation on a radome. These systems also make use of a feedback loop and motors to stabilize the system.
U.S. Pat. No. 3,968,496 to Brunvoll describes a purely mechanical stabilization system which incorporates a counterweight supported in a universal joint bearing. The system includes an elevational and azimuth controller mounted to a platform with a shaft, which is supported by the universal joint bearing. This system makes use of a small mass system, which incorporates a container enclosing two curved tubes which may be filled with liquid and/or small balls. The mass system is mechanically coupled to the platform shaft and is used to stabilize and/or damp the movements of the antenna caused by a ship. The Brunvoll invention includes a servo motor and a momentum wheel driven by a motor as possible accessories to improve the stabilization of the system. Due to the construction of this invention, it is believed to be expensive to produce and subject to high maintenance.
Systems using gyros and/or electronic feedback loops are often quite expensive to manufacture and incur high field service and maintenance costs. A passive mechanical system could significantly reduce costs if adequate stabilization means could be obtained. Previously, designers of mechanical systems have had difficulties designing a system which provides adequate damping to reduce the possibility of oscillation, while at the same time providing adequate decoupling of the antenna from the ship's motion so as to meet the accuracy needs of the radio transmission system.